1. Field of the Invention
This invention relates to a semiconductor device manufacturing method and more particularly to a manufacturing method of a semiconductor device having fine trench isolation.
2. Description of the Related Art
In recent years, as an element isolation region of a semiconductor device, a shallow trench isolation (STI) region is widely used instead of a local oxidation (LOCal Oxidation of Silicon: LOCOS) type element isolation region. The STI region is less subject to mask conversion errors since the “bird's beak” is not grown, unlike the LOCOS region. Further, in the STI region, the isolation region can be formed deeper and the isolation distance between the adjacent active regions can be made large in comparison with the LOCOS region. A semiconductor device having the LOCOS type element isolation region is described in U.S. Pat. No. 5,963,817, for example.
The STI region is advantageous for miniaturization, but some difficult conditions occur when the semiconductor device is further miniaturized.
One of the problems is that the aspect ratio of the STI region becomes higher. The aspect ratio is the ratio of the vertical length to the width of a trench and, for example, it is a value of a fraction using the opening diameter W of a trench 200 as a denominator and the depth D thereof as a numerator as shown in FIG. 41. As the aspect ratio D/W increases, the cross section of the trench becomes a long narrow shape.
In order to further miniaturize the semiconductor device, it is necessary to reduce the width of the STI region, that is, the opening diameter W. At the same time, in order to compensate for an isolation distance between active regions which is reduced by reducing the opening diameter W, it is necessary to make larger the depth of the STI region, that is, the depth D of the trench. As a result, the aspect ratio of the STI region becomes higher.
In the STI region with the enhanced aspect ratio or the STI region having the opening diameter reduced, one of the difficult conditions is that it becomes difficult to fill the trench with an insulating material. For example, as shown in FIG. 42, insulating materials 201 overhang the trenches 200 to cover the openings of the trenches 200. If the openings of the trenches 200 are thus covered and closed, it becomes impossible to deposit the insulating materials 201 in the trenches 200 to make the STI structure incomplete.
Reference Document: U.S. Pat. No. 5,963,817